The present disclosure generally relates to semiconductor devices, and particularly to a method of forming a raised trench metal semiconductor alloy by selective formation of semiconductor material in a trench, and structures for effecting the same.
Advanced semiconductor devices such as field effect transistors employ a trench silicide that is formed selectively at the bottom of each contact trench. During formation of a metal silicide at a bottom of a contact via trench, silicon is consumed from underneath the contact via trench. If the trench silicide overreaches into the underlying source region or the underlying drain region, the trench silicide may be formed too close to the channel of the field effect transistor, resulting in a high leakage current.
While increasing the thickness of raised source and drain regions could alleviate the overreaching of the trench silicide toward the channel region, such a change requires an accompanying increase in the height of a gate stack as well as higher process uniformity during subsequent planarization of a middle-of-line (MOL) dielectric layer at the gate level. Thus, increasing the thickness of the raised source and drain regions is not a practical option for alleviating the problem of a leakage current due to statistical overreaching of a trench silicide during manufacturing.